WEDNESDAY, April 27 (HealthDay News) -- Levels of chemical flame-retardants in the blood of pet dogs are five to 10 times higher than in humans, researchers have found.

In the study, Indiana University scientists checked the levels of polybrominated diphenyl ethers (PBDEs) in the blood of 17 pet dogs who mainly lived indoors. The average blood concentration of the chemicals in the dogs was about 2 nanograms per gram.

The researchers also found that PBDE levels in dog food average about 1 nanogram per gram, which is much higher than levels found in meat and poultry sold for human consumption. This suggests that PBDEs in dog food may come from processing rather than from the food sources.

The study was published online April 18 in the journal Environmental Science & Technology.

PBDEs are used as flame-retardants in a wide range of consumer products, including furniture and electronics. The chemicals can migrate out of the products and enter the environment, according to background information in a university news release.

One particularly hazardous type was voluntarily removed from the U.S. market in 2004, but still lingers in the environment, the researchers noted.

"Even though they've been around for quite a while, we don't know too much about these compounds' toxicological effects on humans or animals," study author Marta Venier, an assistant research scientist in the School of Public Health and Environmental Affairs, said in the news release.

The researchers are exploring whether pets could serve as "biosentinels" for monitoring human exposure to chemicals in the home. In a previous study, the investigators found that pet cats had much lower levels of PBDEs than dogs.

Because their metabolism is better equipped to break down chemicals found in homes, dogs may be better biosentinels than cats, the researchers explained.